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Really basic solar question

 
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So, as you may well figure out from this question, I'm very new to this and don't have a clue what I'm doing.  I have a small 5 in 1 power pack.  I have a Specialty Concept 12 volt, 8 amp automatic sequencing charger.  I want to use a solar panel and this charger to charge my power pack.  The power pack has a 12 volt cigarette lighter type plug I'm going to use to charge it.  It has an 18aH battery.  The plans I saw call for a 45 watt solar panel and a 12 volt, 4 amp charger.  I want to use my 8 amp charger instead.  I don't want to buy a little 45 watt panel, I would rather just buy a 100 or 200 watt one.  So, my question is, can I use a bigger solar panel and the 12 volt, 8 amp charger to charge my power pack without blowing anything up?  Extra points and an apple if you can help me understand how all this works, and whatever I need to know so that I don't have to ask another stupid question next time I want to try something a little different :)
 
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Typical charging rate, current and time for a standard 60Ah automotive AGM battery are 0.1C, 6A and 15h (2hrs-bulk, 8hr-absorption, 5hr-float).
So for your 18Ah AGM battery the charging rate will be 0.1C or 1.8A per hour. If you charge faster than this, it will reduce the lifespan of your battery. Basically you fully discharging or charging your battery in 1hr is very bad for your battery you have to do it slowly over 10hr+. Using up only 1/10 of your capacity per hour. (If you had a LiFePO4 battery you can charge/discharge at 0.5C (0.25C to 1.0C depending on the quality of the battery))

So with your 18AH battery bank that requires 1.8A aka 0.1C. We are already going over by using a 4A solar panel. Luckily we only get that 4A under ideal condition at the equator, with no dust at mid-day sun, cooling wind, perfect temperature, oversize wire gauge, etc, etc. in reality it will actually be 3amp at noon, and closer to 1.5A most of the day. With us only getting 4hrs effectively out of the 12hour day. So that 4A solar panel is effectively 2A (1.8A) for most of the day and it doesn't really harm the battery bank.

Now if you overload that battery bank with 4x what is rated for it will have a very very short life. Also your battery bank can only hold 218WH while a 200W solar panel will produce 800W per day. In such a system you will be wasting alot of energy every day.
 
Trace Oswald
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S Bengi wrote:Typical charging rate, current and time for a standard 60Ah automotive AGM battery are 0.1C, 6A and 15h (2hrs-bulk, 8hr-absorption, 5hr-float).
So for your 18Ah AGM battery the charging rate will be 0.1C or 1.8A per hour. If you charge faster than this, it will reduce the lifespan of your battery. Basically you fully discharging or charging your battery in 1hr is very bad for your battery you have to do it slowly over 10hr+. Using up only 1/10 of your capacity per hour. (If you had a LiFePO4 battery you can charge/discharge at 0.5C (0.25C to 1.0C depending on the quality of the battery))

So with your 18AH battery bank that requires 1.8A aka 0.1C. We are already going over by using a 4A solar panel. Luckily we only get that 4A under ideal condition at the equator, with no dust at mid-day sun, cooling wind, perfect temperature, oversize wire gauge, etc, etc. in reality it will actually be 3amp at noon, and closer to 1.5A most of the day. With us only getting 4hrs effectively out of the 12hour day. So that 4A solar panel is effectively 2A (1.8A) for most of the day and it doesn't really harm the battery bank.

Now if you overload that battery bank with 4x what is rated for it will have a very very short life. Also your battery bank can only hold 218WH while a 200W solar panel will produce 800W per day. In such a system you will be wasting alot of energy every day.



This is for a small portable system used for things like camping or emergency lighting during a power outage, so I'm not worried about wasting energy.  The panel is only connected long enough to charge the battery pack.

I think what you are saying is that a 100 watt panel will work for this, but anything larger will charge the battery too fast and kill it's lifespan, correct?
 
S Bengi
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Given that the battery bank only requires 1.8A (18AH at 0.1C), I think a 50W (2.9A) panel is best, but you could risk it with a 100W(5.7A) solar panel and anything bigger would charge the battery too fast and kill its life.

As for a regular/AC battery charger, I wouldn't go over the 1.8A that the battery bank is rated for.

It's possible that you can expand the battery bank by slapping on some wires and connecting a 40AH 12v batter in parallel. Then you don't have to worry about connecting a 100W solar panel.

Previously you also mentioned a 200W solar panel. Most 250W solar panel are for a 24V battery bank vs 12V battery bank, did you mean a single 200W solar panel or two 100W solar panel for a total of 200W? If it is two 100W solar panels you could actually add a 100AH 12v battery bank to the 18AH one that you have and have even more power/energy.
 
Trace Oswald
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S Bengi wrote:Given that the battery bank only requires 1.8A (18AH at 0.1C), I think a 50W (2.9A) panel is best, but you could risk it with a 100W(5.7A) solar panel and anything bigger would charge the battery too fast and kill its life.

As for a regular/AC battery charger, I wouldn't go over the 1.8A that the battery bank is rated for.

It's possible that you can expand the battery bank by slapping on some wires and connecting a 40AH 12v batter in parallel. Then you don't have to worry about connecting a 100W solar panel.

Previously you also mentioned a 200W solar panel. Most 250W solar panel are for a 24V battery bank vs 12V battery bank, did you mean a single 200W solar panel or two 100W solar panel for a total of 200W? If it is two 100W solar panels you could actually add a 100AH 12v battery bank to the 18AH one that you have and have even more power/energy.



I was looking at both, (2) 100 watt panels, or (1) 200 watt panel.  I really like the idea of adding the 100aH battery bank.  I wouldn't have thought of that, thank you.
 
S Bengi
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https://www.ecodirect.com/Specialty-Concepts-ASC-12-8-p/specialty-concepts-asc-12-8.htm
https://s3.amazonaws.com/ecodirect_docs/SPECIALTY/ASC.pdf
Looking at your charge controller it only supports a max battery connection of 143W (14.3V x 10A), so it will never use up the full 200W of solar panel.  But alot of charger controller allow the an oversize solar array.

The charge controller only support a max open circuit voltage of 26V, so we will have to make sure that the solar panel doesn't exceed this. There are single solar panels that would work such as this https://www.walmart.com/ip/200-WATT-SOLAR-PANEL/615242190
 
Trace Oswald
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S Bengi wrote:https://www.ecodirect.com/Specialty-Concepts-ASC-12-8-p/specialty-concepts-asc-12-8.htm
https://s3.amazonaws.com/ecodirect_docs/SPECIALTY/ASC.pdf
Looking at your charge controller it only supports a max battery connection of 143W (14.3V x 10A), so it will never use up the full 200W of solar panel.  But alot of charger controller allow the an oversize solar array.

The charge controller only support a max open circuit voltage of 26V, so we will have to make sure that the solar panel doesn't exceed this. There are single solar panels that would work such as this https://www.walmart.com/ip/200-WATT-SOLAR-PANEL/615242190



I took your advice and ordered a 50 watt panel instead.  I really need to do a lot more reading before committing to a bigger system.  This one is cheap enough that I can chalk it up to a learning experience while still getting some use out of it.  Thanks for your help with this.
 
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